Means for controlling frequency of an electron tube



0. HEIL May 31, 1966 MEANS FOR CONTROLLING FREQUENCY OF AN ELECTRON TUBE 2 Sheets-Sheet 1 Filed Feb. 24, 1961 AMPLIFIER INVEN TOR. OSKAR HEIL AMPLIFIER ATTORNEY O. HEIL May 31, 1966 MEANS FOR CONTROLLING FREQUENCY OF AN ELECTRON TUBE Filed Feb. 24, 1961 2 Sheets-Sheet 2 AMPLIFIER 3 A 6 Z 3 W. W

w 3 w I m INVENTOR. OSKAR HEIL g ill! AMPLIFIER /XSA ATTORNEY United States Patent 3,254,265 MEANS FOR CONTROLLING FREQUENCY OF AN ELECTRON TUBE Oskar Heil, San Mateo, Calif., assiguor, by mesne assignments, to Varian Associates, a corporation of California Filed Feb. 24, 1961, Ser. No. 91,452 6 Claims. (Cl. 3l55.24)

This invention relates to stabilization of an operating characteristic of electron tubes, and more particularly to a method and means for frequency stabilizing electron tubes in which the operating frequency is temperature sensitive.

Many electron tubes, particularly those of the oscillator type, are sensitive to variations in different characteristics such as operating temperature for example, the effect of such changes being undesirable variations in some other characteristic dependent on the first, such as frequency or oscillation.

The existence of this problem has been recognized by the electronics industry, and various means for providing frequency stability have been utilized, with varying degrees of success. Thus, in the klystron tube are for example, in which resonant cavities of given volume are required for a given operating frequency, variations in temperatures of the cavities results in expansion and contraction thereof and consequent variations in the output frequency. To counteract such undesired expansion and contraction, the prior art has resorted to mechanical contrivances such as expansible and contractible restraining elements and struts arranged to oppose and compensate for frequency drift resulting from temperature variations, or to auxiliary circuit means for accomplishing the same purpose. Examples of such means are adequately disclosed in United States Letters Patent No. 2,294,942, 2,503,266 and 2,515,280.

The disadvantages inherent in these mechanical contrivances include diflicult and expensive fabrication and assembly, inaccuracy of temperature control, time lag between frequency change and compensating counteraction, and a limited range of frequencies which may be adequately controlled. Another disadvantage is that the overall size and weight of the tube being controlled is increased by auxiliary equipment, an important factor where considerations of size and weight determine applicability.

It is therefore the broad object of the present invention to provide a method, and means embodying that method for stabilizing at least one of the operating characteristics of an electron tube in a manner and by means which obviate at least some of the disadvantages enumerated.

As indicated by the prior art, auxiliary sources of power are often used to effect a counteraction to frequency drift resulting from thermal expansion and contraction of frequency determining structure. Such auxiliary sources are expensive, add to circuit complications, and are subject to their own idiosyncrasies. It is accordingly another important object of the invention to interrelate as closely as practicable the cause of such frequency drift with the means for counteracting it.

The problem of thermal expansion and contraction of resonators has been met by the prior art by providing cavities with flexible walls, interconnected in a manner to effect displacement of the flexible walls in a direction to maintain the volume of the cavity constant. Cavities of this type, however, are particularly sensitive to variations in pressure, and are therefore unreliable in applications such as rocketry where extremes in both temperature and pressure are encountered. A still further object of the invention, therefore, is the provision of a frequency stable electron tube unaffected by extremes in ambient temperature and/or pressure.

Since remote control of an auxiliary power source such Fee as used by the prior art to counteract frequency drift of an electron tube is difficult to achieve, it is a still further object of the invention to utilize the electrons within the tube as a source of energy to effect a counteraction of such frequency drift.

The frequency of a high frequency device such as a klystron oscillator is particularly sensitive to variations in temperature of the resonant cavities. Such tubes are particularly useful in telemetering applications, but such use requires extremely close control of frequency drift. Fluctuations of temperature above and below fixed, narrow limits result in frequency drift out of the acceptable range. It is therefore a still further object of the invention to provide a klystron oscillator in which the temperature of the radio-frequency interaction structure or frequency determining network is monitored, and counteracting means responsive to the monitoring means are provided to maintain the temperature of the structure substantially constant.

Still another object of the invention is the provision of a high-frequency klystron oscillator in which the temperature of the radio-frequency determining structure is monitored, and means are provided interconnected with the monitoring means for effecting varying degrees of deflection of the electron beam to maintain the temperature of the structure constant.

Frequency instability also arises from mechanical vibration of parts within the envelope such as drift tubes, movement of which varies the effective spacing therebetween. A still further object of the invention therefore is the provision of a klystron oscillator in which fabrication and assembly of parts may be effected by mass production technique to produce a tube singularly rugged and free from mechanical vibration of its parts.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will become apparent from the following description and the drawings. It is to be understood that the invention is not limited to the embodiments of methods or means described and illustrated, but may be incorporated in other embodiments within the scope of the appended claims.

Broadly considered, the invention finds application in any electron tube in which there is a flow of electrons, and in which an operating characteristic, such as frequency, is sensitive to variations in some other operating characteristic or parameter, such as temperature. Controlled deflection of the electrons in such tubes in response to variations in the operating characteristic desired to be controlled is utilized to maintain such variations within close limits. This method of control is particularly useful in radio-frequency oscillators utilizing resonating output circuits, the resonating frequencies of which are sensitive to fluctuations in temperature. The invention in one of its aspects therefore comprises utilization of the inherent kinetic energy of the electrons to maintain the oscillating frequency of the output circuit constant. By monitoring the temperature of the output circuit, as by means of a thermal sensing device such as a thermocouple, or by monitoring the frequency directly, deflection of the electrons out of their normal course may be effected in response to the intelligence secured by such monitoring. Such deflection results in the electrons being caused to impinge against associated tube walls, causing the walls thereof to vary in temperature. The variation in temperature or frequency, monitored as it is by the thermal or other electronic sensing device, results in a closely controlled decrease or increase in the amount of electron deflection. To effect deflection, electrical energy from the thermocouple or other sensing device is amplified, controlled and impressed on electrostatic or electromagnetic deflecting means associated with the stream of electrons or electron beam in a manner to effect its deflection.

The unitary, integral relationship of the tube parts contributes to a rapid and uniform distribution of heat over the radio frequency determining structure to maintain the temperature and therefore the frequency constant.

Referring to the drawings:

FIGURE 1 is a half sectional view of a floating drift tube klystron constructed according to one embodiment of the invention, in which electrostatic probe means are utilized to effect deflection of electrons.

FIGURE 2 is a fragmentary half sectional view of another embodiment utilizing electrostatic deflection means.

FIGURE 3 is a fragmentary half sectional view of an embodiment of the invention which utilizes electromagnetic probe means for effecting deflection of the electrons.

FIGURE 4 is a fragmentary half sectional view of still another embodiment utilizing electromagnetic means for effecting deflection of the electrons.

In terms of greater detail, the invention, as embodied in a floating drift tube type klystron oscillator comprises an evacuated dielectric and metallic envelope symmetrical about a longitudinal axis and including a hollow cylindrical electron gun section 2, a radio frequency interaction section 3 hermetically united at one end to the gun section, and a collector assembly section 4 integrally and hermetically united to the radio frequency interaction section on the end thereof remote from the gun section.

In a tube of this type, it is important for frequency stability that its construction be especially rugged and free from mechanical vibrations which can also produce frequency drift. For economy of manufacture, it is also important that there be as few parts as possible and that the configuration of parts be susceptible of mass production and assembly. Accordingly, the tube is designed to permit sub-assembly of electron gun, radio frequency structure and collector assembly as separate entities which may then be integrally joined into a composite whole. The hollow cylindrical electron gun section therefore comprises a tubular metallic envelope portion 6 of heavy cross-section symmetrical about a longitudinal axis and having intermediate its ends an integral transversely extending wall 7, centrally apertured to receive a drift tube section 8 extending therethrough. The drift tube section 8 also constitutes the accelerating anode of the electron gun, and in use is electrically connccted to a suitable electrical potential.

Housed within the envelope on one side of the wall 7, and cooperatively related and proportioned to project an electron beam along the axis of the envelope, are a focus electrode 9 and a cathode 12, each appropriately electrically insulated from each other and from the envelope by dielectric rings 13 and 14, respectively. For maximum rigidity, the cathode and a heating coil 16 therefor, are unitized and demountably secured to the envelope by a clamp bracket 17 fastened to annular shoulder 18 by screws 19. Suitable leads 21 extend hermetically through dielectric end plate 22, sealed across the end of envelope portion 6 by sealing rings 23 and 24, the leads being adapted to be appropriately connected to the focus electrode and heater coil, but here, in the interest of clarity, being shown terminated within the envelope adjacent end plate 22. The inner peripheral portions of the sealing rings are brazed, respectively, to the envelope portion 6 and the dielectric end plate 22, while the outer peripheral edges of the rings are heliarc welded at 26 to form a final hermetic seal capable of being taken apart or opened and subsequently re-sealed.

From the foregoing it will be apparent that a rugged electron gun structure has been provided, and that the design and arrangement of the different parts contribute to the efficient initial assembly of the electron gunstructure. Additionally, the demountability of the cathodeheater package, coupled with the take-apart character of final seal 26, makes it practicable to re-gun the tube, thus materially reducing replacement costs.

As shown in the drawings, the envelope portion 6 is formed with a cylindrical flange 27 on its end remote from end cap 22. The flange cooperates with wall 7 and a second metallic cylindrically flanged wall 28 axially spaced and substantially parallel to wall 7 to form resonant cavity 29. Transverse wall 28 is provided with oppositely extending cylindrical flanges 31 and 32, the former, together with flange 27 being rabbcted as shown to provide selfjigging alignment of the parts. A drift tube segment 33 is supported by radially extending spokes 34 cooperating with flanges 27 and 31 in axial alignment with but spaced from drift tube segment 8 a small amount to provide a beam modulating interaction gap. For ease of alignment of the drift tube section, the flange 31 is appropriately grooved to receive the outer ends of spokes 34 which are brazed into the envelope wall. Additionally, Where desired for additional rigidity, spokes 34 may be slightly bowed to resist vibration even more eflcctively.

The resonant cavity is completed by a centrally positioned drift tube segment 36 aligned with drift tube segments 33 and 8. Integral cylindrical flange 32 extending from wall 28 forms a cylindrical wall portion of the tube envelope and a portion of output cavity 37. The output cavity is defined by wall 28, flange 32, and a transverse wall 38 appropriately spaced from wall 28 and rigidly brazed to flange 32. Drift tube segment 39, supported on wall 38, is axially aligned with the other drift tube segments within the envelope. A suitable coupling loop 41 extends insulatingly through the envelope wall into the output cavity to couple electromagnetic energy therefrom.

A comparison of the figures of the drawing will indicate that the construction of each of the four embodiments is identical through the output cavity 37. In the embodiments illustrated in FIGURES 1, 3 and 4, the radio-frequency interaction structure comprised of resonant cavities 29 and 37, is integrally and hermetically connected to the collector assembly 4 by a cylindrical, thin metallic shell 42 forming a part of the evacuated envelope and electrically connecting the collector to the radio-frequency structure. The shell is preferably formed from a low heat conductivity metal such as that sold under the trade name Hastalloy. As shown, an inturned flange 43 on one end of the shell is brazed to the rabbeted periph ry of wall 38, while the other end of the shell is brazed to the collector assembly. It is noted that While We have chosen to show the shell 42 as preferably having a self-sustaining thickness, we are aware that shell 42 could be formed by metalizing a conductive layer on the outer periphery of a dielectric tube such as that shown in FIGURE 2.

Axially aligned with the drift tube segments, and form ing part of the collector assembly, is a truncated conical metallic shell 46 having its apex end 47 spaced from drift tube 39. The base end of the conical collector shell is provided with a radially extending flange 48 brazed adjacent its outer periphery to shell 42 and collector body 49. It will thus be seen that the collector assembly constitutes an effective trap for electrons passing thereinto, and that thin shell 42, whether in the form illustrated or as a metalized sheath, forms a heat resistive link or heat darn between the collector and radio-frequency structure. The radio-frequency structure is therefore substantially thermally isolated but electrically connected to the collector. To secure the tube rigidly on a supporting structure, radially extending flange 51 is provided extending from the cylindrical periphery of collector 49.

In the embodiment illustrated in FIGURE 2, the shell 42 has been eliminated and the radio-frequency structure is integrally and hermetically united to the collector assembly by a tubular dielectric envelope portion 52 metalized at opposite ends and preferably formed from thermally resistive alumina ceramic to provide electrical and thermal insulation between collector and radio-frequency structure. It is in conjunction with such a tubular dielectric portion that a metalized coating thereon could function to electrically connect the collector assembly to the frequency determining network.

In normal operation of the tube, the electron beam projected by the electron gun will pass through the cavities and drift tube sections and a major portion thereof will be collected by the collector, by which the energy of the beam will be dissipated as heat. Since in each embodiment the collector is thermally isolated from the radiofrequency interaction structure, means are provided for maintaining the radio-frequency structure at a substantially constant temperature, selected to exceed any ambient temperature likely to be encountered, without dependence on flow of heat from the collector to the radio-frequency structure. As previously explained, the frequency stability of the device is dependent to a large extent on the volume of the cavities remaining constant, but thermal expansion and contraction of the cavity walls effects variations in such volume, resulting in frequency drift. It will of course be obvious that the parts are designed to provide the proper volume for a selected frequency at the desired or selected operating temperature. Spokes 34, while shown perpendicular to the drift tube, may be inclined and possess a configuration such that thermal expansion of the cavity results in appropriate compensating movement of drift tube 33.

To maintain the temperature of the radio-frequency structure constant, at least insofar as frequency instability is caused by thermal expansion and contraction, the temperature thereof is monitored, preferably continuously, by an appropriate heat sensing device such as thermocouple 53, operatively attached to the radio-frequency structure in a manner to respond to heat therefrom. The thermocouple may be connected to an amplifier 54, and the output of the amplifier operatively connected by appropriate lead means 55 to beam deflecting means mounted on the envelope and operatively associated with the beam in a manner to effect deflection of electrons onto surrounding structure.

In the embodiment shown in FIGURE 1, the output of the amplifier is connected to a probe 56 which extends insulatingly into the envelope and terminates in a free end adjacent the beam path. When the temperature of the radio-frequency structure decreases fro-m the selected operating temperature, the variation in current flow through the thermocouple results in the probe being electrostatically charged an appropriate amount. Electrons from the beam will accordingly be deflected by such electrostatic charge and impinge on the adjacent wall 38. If deflection of the beam is such as to cause all of the electrons to impinge on the radio-frequency structure, the tube will return to its selected operating temperature very quickly and deflection of the beam may then be terminated or diminished. If deflection is eliminated, all the electrons will be collected and the radio-frequency structure will either remain at its selected operating temperature or will tend to cool below such temperature. If it cools, deflection of the beam is again automatically effected to bring the temperature up to the selected level. It will be understood that while a continuously compensating system is preferred, it is feasible to correlate compensating action with a range of values having minimum and maximum limits.

In FIGURE 2, the collector is both thermally and electrically isolated from the radio-frequency structure, and the output of the amplifier is connected so as to electrostatically charge the entire collector in an appropriate sign to either collect or deflect the electron beam. When deflected, the beam will impinge on the wall 38 as before and heat the tube. Such electrostatic charging of the collector is in response to and correlated to the temperature of the radio-frequency interaction structure as sensed by the thermocouple or other heat sensing device as previously described.

FIGURES 3 and 4 embody electromagnetic probes 57 and 57', respectively, each mounted on the envelope and having its inner end associated with the beam in a manner to selectively effect deflection of electrons. A coil 58 about the outer end of each probe and operatively connected to the amplifier generates a magnetic field in the proximity of the inner end of the probe which effectively deflects the beam so that it impinges on the adjacent wall 38. In FIGURE 3, the probe is shown schematically, extending transversely into and supported on shell 42, and terminates in proximity to the beam between the output cavity and collector. In FIGURE 4, the probe extends through and is supported on the collector, and terminates in a conically tapered point 59 substantially flush with the inner apex end 47 of collector shell 46. In both embodiments, energizing the coil 58 results in a magnetic field being formed about the inner end of the probe, causing electrons in the beam to be deflected onto adjacent structure thus causing the tube to heat. The intensity of the magnetic field is determined by the amount of current flowing through the coil, which in turn is controlled through the amplifier by the sensing thermocouple fixed on the radio-frequency structure. In use, the monitoring and deflecting means balance the temperature variations within very close limits and ensure a minimum frequency drift.

I claim:

1. An electron tube comprising an electron gun for projecting a beam of electrons, a frequency determining interaction section operatively disposed for interaction with said beam, said interaction section comprising all rigid wall means all rigidly interconnected to prevent deformation thereof and thus prevent change of the frequency defined thereby, means operable to selectively deflect electrons from said beam to cause some of the electrons to reverse their direction of travel to transfer heat energy from said beam to said interaction section, said interaction section being constructed to provide rapid and uniform distribution of heat over the interaction means whereby heat from the beam can maintain the entire interaction section at a substantially uniform temperature to prevent change of the frequency defined thereby, means for sensing the temperature of said interaction section, and means responsive to the temperature sensing means to energize said deflecting means to cause deflection of electrons in the beam.

2. An electron tube as claimed in claim 1 in which said deflecting means is a collector electrode, and wall means substantially thermally insulating said collector from said interaction section.

3. An electron tube as claimed in claim 1 in which said tube comprises an end electrode aligned with the electron beam projected by said gun, and said deflecting means comprises an electrostatic probe interposed be tween said interaction section and said end electrode for deflecting electrons directly onto said interaction section.

4. An electron tube as claimed in claim 1 in which said tube comprises an end electrode aligned with the electron beam projected by said gun, and said deflecting means comprises an electromagnetic probe interposed between said interaction section and said end electrode for deflecting electrons directly onto said interaction section.

5. An electron tube as claimed in claim 1 in which said deflecting means is positioned adjacent one end of said interaction section, and said temperature sensing means is positioned adjacent the opposite end of said interaction section.

6. An electron tube comprising an electron gun adjacent one end for projecting a beam of electrons, a collector electrode adjacent the other end of the electron tube and aligned with the beam of electrons projected by said gun, a frequency determining interaction section operatively disposed between said gun and said collector and having an input gap and an output gap, said interaction section comprising all rigid wall means all rigidly interconnected to prevent deformation thereof and thus prevent change of the frequency defined thereby, said gun and interaction section and collector electrode being normally operable to project the beam from the gun onto the collector electrode with substantially no electrons being intercepted en route, beam deflecting means in the tube selectively operable to deflect electrons from said beam onto a portion of the tube in advance of said collector to transfer heat energy from said beam to said interaction section, said interaction section being constructed to provide rapid and uniform distribution of heat over the interaction section whereby heat from the beam can maintain the entire interaction section at a substantially uniform temperature to prevent change in the frequency defined by the interaction section, means for sensing the temperature of said interaction section, and means responsive to the temperature sensing means to energize said deflecting means to cause deflection of electrons in the beam.

References Cited by the Examiner UNITED STATES PATENTS 8 2/1952 Fernsler 331-88 6/1954 Woodyard et a1 3l55 X 10/1954 Beaumont 328-3 X 8/1956 Norton 3155.25

4/1957 Janis 3155.18

9/1959 Preist et a1. 315-5.46 X

9/1959 Steiner 313-11 X 7/1962 Haegele et a1. 3155.2l 11/1962 Rockwell 315-534 FOREIGN PATENTS 5/1947 Canada.

DAVID J. GALVIN, Primary Examiner.

ARTHUR GAUSS, Examiner.

20 R. SEGAL, Assistant Examiner. 

1. AN ELECTRON TUBE COMPRISING AN ELECTRON GUN FOR PROJECTING A BEAM OF ELECTRONS, A FREQUENCY DETERMINING INTERACTION SECTION OPERATIVELY DISPOSED FOR INTERACTION WITH SAID BEAM, SAID INTERACTION SECTION COMPRISING ALL RIGID WALL MEANS ALL RIGIDLY INTERCONNECTED TO PREVENT DEFORMATION THEREOF AND THUS PREVENT CHANGE OF THE FREQUENCY DEFINED THEREBY, MEANS OPERABLE TO SELECTIVELY DEFLECT ELECTRONS FROM SAID BEAM TO CAUSE SOME OF THE ELECTRONS TO REVERSE THEIR DIRECTION OF TRAVEL TO TRANSFER HEAT ENERGY FROM SAID BEAM TO SAID INTERACTON SECTION SAID INTERACTION SECTION BEING CONSTRUCTED TO PROVIDE RAPID AND UNIFORM DISTRIBUTION OF HEAT OVER THE INTERACTION MEANS WHEREBY HEAT FROM THE BEAM CAN MAINTAIN THE ENTIRE INTERACTION SECTION AT A SUBSTANTIALLY UNIFORM TEMPERATURE TO PREVENT CHANGE OF THE FREQUENCY DEFINED THEREBY, MEANS FOR SENSING THE RESPONSIVE TO THE TEMPERATURE ACTION SECTION, AND MEANS RESPONSIVE TO THE TEMPERATURE SENSING MEANS TO ENERGIZE SAID DEFLECTING MEANS TO CAUSE DEFLECTION OF ELECTRONS IN THE BEAM. 